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Normalization of the modulation transfer function: The open‐field approach
Author(s) -
Friedman S. N.,
Cunningham I. A.
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2977536
Subject(s) - normalization (sociology) , optical transfer function , spectral leakage , transfer function , spatial frequency , region of interest , image resolution , optics , physics , mathematics , algorithm , artificial intelligence , computer science , electrical engineering , fast fourier transform , sociology , anthropology , engineering
The modulation transfer function (MTF) is widely used to describe the spatial resolution of x‐ray imaging systems. The MTF is defined to have a zero‐frequency value of unity, and it is common practice to ensure this by normalizing a measured MTF curve by the zero‐frequency value. However, truncation of the line spread function (LSF) within a finite region of interest (ROI) results in spectral leakage and causes a reduction in the measured MTF zero‐frequency value equal to the area of truncated LSF tails. Subsequent normalization by this value may result in inflated MTF values. We show that open‐field normalization with the edge method produces accurate MTF values at all nonzero frequencies without need for further normalization by the zero‐frequency value, regardless of ROI size. While both normalization techniques are equivalent for a sufficiently large ROI, a 5% inflation in MTF values was observed for a CsI‐based flat‐panel system when using a 10 cm ROI. Use of open‐field normalization avoids potential inflation caused by zero‐frequency normalization.